Field of the Invention
The present invention is in the technical field of energy storage devices. More particularly, the present invention is in the technical field of rechargeable batteries using an iron electrode.
State of the Art
Iron electrodes have been used in energy storage batteries and other devices for over one hundred years. Iron electrodes are often combined with a nickel base cathode to form a nickel-iron battery. The nickel-iron battery (Ni—Fe battery) is a rechargeable battery having a nickel (III) oxide-hydroxide cathode and an iron anode, with an electrolyte such as potassium hydroxide. The active materials are held in nickel-plated steel tubes or perforated pockets. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have a very long life even if so treated. It is often used in backup situations where it can be continuously charged and can last for more than 20 years. Due to its low specific energy, poor charge retention, and high cost of manufacture, however, other types of rechargeable batteries have displaced the nickel-iron battery in most applications.
The ability of these batteries to survive frequent cycling is due to the low solubility of the reactants in the electrolyte. The formation of metallic iron during charge is slow because of the low solubility of the ferrous hydroxide. While the slow formation of iron crystals preserves the electrodes, it also limits the high rate performance. These cells charge slowly, and are only able to discharge slowly. Nickel-iron cells should not be charged from a constant voltage supply since they can be damaged by thermal runaway. The cell internal voltage drops as gassing begins, raising the temperature, which increases current drawn and so further increases gassing and temperature.
The methods used in the preparation of the iron electrode (anode) have contributed to the low performance versus cost of the Ni—Fe battery.
The technology of preparing iron electrodes is well known and the current preferred process for making these electrodes is a pocket design. The pocket design is not cost effective and is complex in its manufacture. Pocket design electrodes are also difficult to produce in high volumes, and the energy and power utilization from this design is low. What is needed is a low cost, high volume, high quality and high performance iron electrode design and manufacturing process.